A typical fluid treatment element, for many uses, comprises a hollow, generally cylindrical, filter element with appropriate end caps to direct a fluid, e.g., a gas or liquid, through the filter medium of the filter element. The precise nature of the filter medium will vary with the specific treatment to be given the fluid, and, to that end, the filter element may include a demineralizer or sorbent for separating ionic or chemical components in addition to the filter medium for removing particulates.
The fluid to be treated is generally forced to flow inwardly from the exterior to the interior of such a fluid treatment element, although there is no requirement that such be the case. It should be noted that irrespective of the normal flow of fluid through the fluid treatment element, it is not unusual to have the fluid flow reversed, either accidentally (e.g., due to a surge in fluid pressure downstream from the filter element) or intentionally (e.g., to flush an accumulated cake of particulate matter from the surface of the filter element).
While tubular fluid treatment elements typically have a uniform pore structure, one such fluid treatment element, the Profile.RTM. filter element (Pall Corporation), utilizes a filter medium of a graded or tapered porosity whereby the pore size of the filter medium decreases in the direction of fluid flow. The filter medium of the Profile.RTM. filter element comprises a continuous series of fibers of varying diameter which are layered upon themselves to form a filter medium of a graded pore structure with a constant void volume. Such a medium is disclosed in U.S. Pat. Nos. 4,594,202 and 4,726,901.
A variety of other fluid treatment element configurations have been proposed and utilized over the years, including string wound filter elements, sintered stainless steel powder filter elements, multiple layer filter elements, spiral wrapped fluid treatment elements, and helical wrapped filter elements. Despite these various configurations, there remains a need for a tubular fluid treatment element characterized by a relatively high strength, low pressure drop, high dirt capacity, and long life, and which is nonetheless economical to manufacture and utilize.
It is an object of the present invention to provide such a fluid treatment element. These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.